Structural Studies of Ordering in the (Pb 1‐x Ba x )(Mg 1/3 Nb 2/3 )O ₃ Crystalline Solution Series

The ordered structures of the (Pb 1‐ x Ba x )(Mg 1/3 Nb 2/3 )O 3 crystalline solution series were investigated by selected area electron diffraction (SAED) and high‐resolution electron microscopy (HREM). At low Ba contents (e.g., x < 0.40), the ordered structure was found to be isostructural with Pb(Mg 1/3 Nb 2/3 )O 3 , with a doubled unit cell characterized by 1/3{111} superlattice reflections. At higher Ba contents (e.g., x > 0.60), the ordered structure was characterized by 1/3{111} superlattice reflections. For intermediate Ba contents (e.g., x ‐ 0.60), diffuse scattering along the {111} between diffuse 1/2{111} and 1/3{111} reflections was observed. The ordering is attributed to the distribution of the B‐site cations between multiple sublattices. Strong fluctuations in the B‐site cation ratio between ordered and disordered regions are believed not to exist; however, the possibility of weak fluctuations is consistent with the observed lattice images.